<?php
    
    function checkSignature(){
        $signature = $_GET["signature"];
        $timestamp = $_GET["timestamp"];
        $nonce = $_GET["nonce"];
        $token = 'Welink168';
        $tmpArr = array($token, $timestamp, $nonce);
        sort($tmpArr, SORT_STRING);
        $tmpStr = implode( $tmpArr );
        $tmpStr = sha1( $tmpStr );
        if( $tmpStr == $signature ){
            return true;
        }else{
            return false;
        }
    }
    
    if ( checkSignature() ) {
        echo $_GET['echostr'];
    }

 ?>